1. Field of the Invention
The present invention generally relates to the field of manufacturing and more specifically, to the manufacture of chromed vehicle bumpers.
2. Background of the Invention
A vehicle bumper is a component attached to the front and rear ends of a vehicle to serve as an energy dissipation device in a collision, thereby protecting the vehicle body and the driver.
Vehicle bumpers are generally formed of steel which must undergo several processes prior to chroming. By way of background, steel must be initially processed through a hot strip mill. Steel slabs are heated to approximately 2275 degrees Fahrenheit and are delivered from the furnaces to an 80 inch hot strip rolling mill so that the strips are rolled to a nominal thickness of 9¼ inches. The slabs are discharged from the furnace with a nominal thickness of 9¼ inches and delivered to vertical scale breaker within seconds. The vertical scale breaker reduces the bar to the desired width and helps break up the oxide layer formed on the slab surfaces during reheating. The bar is then sprayed with high pressure (approximately 1850 psi) descale spray water to mechanically clean the bar and force any freshly formed scale off of the bar.
A harder oxide layer also called scale forms on the outside of the strip during the final stages of the hot rolling process. The scale adversely affects the quality of any finish coating applied to the steel. Typically, either sulphuric or hydrochloric acid may be used on a pickle line. The strip may be immersed in a number of acid baths to remove the oxide scale. The acid bath may be combined with an electric current (electrolytic pickling) to remove the oxide scale. After immersion in the acid baths, the strip is generally rinsed in water and dried in warm air before being coiled again.
Referring now to FIG. 1, a flowchart demonstrating the steps of manufacturing a chromed bumper from steel strips is illustrated. The strip undergoes the cold rolling operation 52 which involves passing the material through narrow rolls. The cold rolling process generally requires several passes back and forth over the strip by a Tandem Mill and a Temper Mill such that the steel gradually becomes harder and is said to be cold hardened. The strip is cold rolled through a temper mill and a tandem mill to reduce the width/thickness of the steel strips and then the strip is slit and sheared 54 into blanks. The blanks are generally polished 56 using a sand paper belt and then cleaned 58 and inspected to determine whether an adequate surface finish was attained. A drawback of using a sand paper belt is that this polishing method leaves linear scratch marks on the steel thereby reducing the quality of the surface finish.
Once the blanks are polished with the sand paper belt, the blanks are coated 60 with Zinc Phosphate and a dry film lube to prepare the blank for stamping. After forming or stamping 62 the bumpers, the bumpers are cleaned and buffed 64 to ensure that film from the zinc phosphate and dry film lube is removed and treated 65 to remove the zinc phosphate and dry film lube. The bumper surface is then electroplated 66 with nickel and then chromed.
The prior art process to manufacture a vehicle bumper is not only time-consuming and expensive due to the cleaning and polishing requirements, but also the polishing process does not provide a homogenous surface for chroming, nor is the surface texture repeatable, ordered and deterministic.
Consequently a need has developed for an efficient means of manufacturing bumpers which reduces cost and manufacture time while improving the surface finish of the bumper for the chroming process.